KR100974092B1 - Conductive paste including a carbon nanotube and printed circuit board using the same - Google Patents

Abstract

The present invention provides a conductive paste including carbon nanotubes and a printed circuit board using the same. The present invention has excellent electrical conductivity without losing the inherent characteristics of carbon nanotubes, and a conductive paste that can be simultaneously implemented in XY interconnection and Z-interconnection of a printed circuit board using the carbon nanotubes, and a printed circuit using the same. Provide a substrate

Carbon nanotubes, low melting point metal alloys, conductive pastes, printed circuit boards

Description

Conductive paste including a carbon nanotube and printed circuit board using the same}

The present invention relates to a conductive paste containing carbon nanotubes and a printed circuit board using the same.

At present, the connection between electronic devices and components and the electrical connection between upper and lower layers mainly use copper (Cu) in consideration of resistivity characteristics and economic aspects. Experimental results show that when the cross-sectional area of the implemented circuit line width is smaller than the mean free path (MFP) of electrons in the bulk metal, the resistivity in the circuit is larger than the specific resistivity of the metal. It is known to increase.

The MFP of copper is 40 nm. Therefore, theoretically, when implementing a circuit having a cross-sectional area smaller than this value, the inherent resistivity characteristic of copper cannot be expected. This phenomenon is, according to the literature, attributed to electron surface scattering and grain-boundary scattering. That is, since a metal conductive paste such as copper has a disadvantage in that it is difficult to apply to a microcircuit, the need for a paste to replace the metal conductive paste is increasing.

Carbon nanotubes (CNTs) are generally several nm in diameter, which is advantageous for applications in ultra-fine wiring. In addition, the maximum allowable current of carbon nanotubes is about 1000 times greater than copper (copper: 10 ⁶ A / cm ² , CNT: 10 ¹⁰ A / cm ² ). Therefore, research is being actively conducted to use carbon nanotubes in the process of connecting the signal wiring (XY interconnection) of the circuit board and the copper foil signal layer (Z-interconnection) above and below the circuit board instead of a metal such as copper. .

In order to implement the X-Y interconnection, an attempt was made to implement carbon nanotubes in a desired pattern form by applying artificial force to carbon nanotubes by using AFM (Atomic Force Microscopy) tips. However, in the process of bending carbon nanotubes, a problem of losing the inherent characteristics (such as ductility or elasticity) of carbon nanotubes has been shown. So, research on implementing X-Y interconnection has not made much progress at present.

However, research on the Z-interconnection between copper foil signal layers above and below the circuit board is relatively active. Z-interconnection requires growing carbon nanotubes to a certain height. Most of this growth is using the Chemical Vapor Deposition (CVD) process.

 However, using the CVD process, i) a high process temperature of 500 to 800 ° C. is required, and ii) a material used as a substrate is limited due to the high process temperature, and iii) a batch process. ) Increases the time needed for mass production of electronics, i.e. lead-time, iv) operation is limited in the vacuum chamber, and v) expensive The disadvantage is the need for a manufacturing process.

The present invention has excellent electrical conductivity without losing the inherent characteristics of carbon nanotubes, and a conductive paste that can be simultaneously implemented in XY interconnection and Z-interconnection of a printed circuit board using the carbon nanotubes, and a printed circuit using the same. It is for providing a substrate.

According to one aspect of the present invention, the present invention provides a conductive paste comprising a carbon nanotube, a low melting point metal alloy and a binder.

In one embodiment of the present invention, the conductive paste may include 70 to 90% by weight of the carbon nanotubes, 1 to 25% by weight of the low melting point metal alloy, and 1 to 15% by weight of the binder.

The conductive paste may further include metal particles, and the metal particles may further include 1 to 10 wt%.

The metal particles may be selected from the group consisting of silver, copper, tin, indium, nickel and mixtures thereof.

The carbon nanotubes may be selected from the group consisting of single walls, multi walls, and mixtures thereof.

The low melting point metal alloy may be an alloy including two or more selected from the group consisting of tin, silver, bismuth, indium and cadmium.

The low melting point metal alloy may be any one selected from an alloy consisting of tin / bismuth, bismuth / tin / cadmium, indium / tin and indium / tin / bismuth.

The tin / bismuth alloy is an alloy composed of 40-45 wt% tin and 60-55 wt% bismuth; The bismuth / tin / cadmium alloy is an alloy consisting of 45-50 wt% bismuth, 15-40 wt% tin and 15-40 wt% cadmium; The indium / tin alloy is an alloy composed of 50 to 70% by weight of indium and 50 to 30% by weight of tin; And the indium / tin / bismuth alloy may be an alloy consisting of indium 5-30% by weight, tin 30-60% by weight and bismuth 25-45% by weight.

The binder may be selected from the group consisting of thermosetting resins, thermoplastic resins, UV curable resins and radical curable resins, and mixtures thereof.

The thermosetting resin may be selected from the group consisting of epoxy resins, cyanate ester resins, bismaleimide resins, polyimide resins, benzocyclobutene resins, phenol resins, and mixtures thereof.

The thermoplastic resin may be selected from the group consisting of liquid crystal polyester resins, polyurethane resins, polyamideimide resins, and mixtures thereof.

The conductive paste further comprises an additive selected from the group consisting of dyes, pigments, thickeners, lubricants, antifoams, dispersants, leveling agents, brighteners, thixotropic agents, flame retardants, oxide removers, organic fillers, inorganic fillers and mixtures thereof. can do.

According to another aspect of the present invention, the present invention provides a printed circuit board comprising the above-mentioned conductive paste.

In accordance with the present invention, the conductive paste including the carbon nanotubes and the low melting point metal alloy has excellent electrical conductivity due to reduced specific resistance. In addition, the conductive paste according to the present invention can be implemented simultaneously in the X-Y interconnection and Z-interconnection of the printed circuit board using the carbon nanotubes, without losing the inherent characteristics of the carbon nanotubes.

Carbon nanotubes have excellent electrical properties when compared with other materials as shown in Table 1 below.

Physical characteristics Carbon nanotubes Comparative substance density 1.33-1.40 g / cm ³ 2.7g / cm ³ (Aluminum) Current density 1 × 10 ⁹ A / cm ² 1 × 10 ⁶ A / cm ² (copper cable) Thermal conductivity 6000 W / mk 400 W / mk (copper) Resistivity 1 × 10 ^-10 Ωcm 1.72 × 10 ^-6 Ωcm (copper)

As shown in Table 1, the carbon nanotubes have better electrical properties than metal materials having relatively high electrical conductivity or specific resistance, such as aluminum and copper. Therefore, when using such carbon nanotubes as the conductive paste material, it is possible to lower the resistance generated during the electrical conduction between the layers of the circuit pattern. In addition, the thermal conductivity is also excellent, it can effectively release the heat inside the printed circuit board to the outside.

The present invention uses the carbon nanotubes and Low Melting Point Alloy (LMPA). In this case, it is possible to combine the low melting point metal components with the carbon nanotubes by melting the low melting point metal alloy. At the same time, metal bonding with the low melting point metal alloy, the carbon nanotubes, and the copper foil layer of the substrate is possible. By such metal bonding, the conductive paste according to the present invention reduces specific resistance and improves electrical conductivity.

In the conventional hole plugging process, there are problems of resistivity and electrical resistance of the paste. In order to solve this problem, a method of filling the paste after forming an electrically conductive metal layer by electrolessly or electroplating the inner wall of the hole was used.

Since the conductive paste of the present invention contains a carbon nanotube and a low melting point metal alloy, the metal reaction between the metal particles and the carbon nanotube interface can be expected to solve the above-mentioned problems. In addition, the conductive paste of the present invention can simultaneously implement X-Y and Z-interconnection through the printing process while maintaining the intrinsic properties of carbon nanotubes at a low temperature of 200 ℃ or less. In general, the X-Y interconnection and Z-interconnection means the interconnection as shown in FIG. 17.

The conductive paste according to the present invention may include a carbon nanotube, a low melting point metal alloy, and a binder.

In one embodiment of the present invention, the conductive paste may include 70 to 90% by weight of carbon nanotubes, 1 to 25% by weight of a low melting point metal alloy, and 1 to 15% by weight of a binder. When the weight of the carbon nanotubes is less than 70% by weight or more than 90% by weight, the electrical conduction properties of the carbon nanotubes may not be generated by percolation theory. In addition, when the low melting point metal alloy is used in less than 1% by weight, the amount of metal that can be dissolved is small so that the desired solid solution (Inter Metallic Compound, IMC) is not formed. Can be. In addition, when the content of the binder is less than 1% by weight, a problem of inferior adhesion may occur, and when the content of the binder exceeds 15% by weight, a problem of inferior electrical conductivity may occur.

The conductive paste may further include metal particles, preferably 1 to 10% by weight. If the metal particles are used in less than 1% by weight or in excess of 10% by weight, the conductive properties may not occur due to the penetration theory.

The metal particles may be selected from the group consisting of silver, copper, tin, indium, nickel, and mixtures thereof, but are not necessarily limited thereto. It is preferable that the said metal particle contains 0.1 to 3 weight% of oxygen content, More preferably, it is 0.2 to 2.5 weight%, More preferably, it is 0.3 to 2 weight%. If it is in this range, the ion migration resistance, electroconductivity, electroconductive connection reliability, and dispersibility to a binder of a metal particle will become favorable.

In one embodiment of the present invention, the carbon nanotubes may use a single wall, multi-wall or a mixture thereof.

The low melting point metal alloy used by this invention means the alloy composition whose melting point is 200 degrees C or less. Since the melting point of the low-melting-point metal alloy is low, it begins to melt before the binder described below, thereby enabling mutual contact with the carbon nanotubes and the copper foil layer of the substrate.

That is, the low melting metal alloy of the present invention serves to reduce the contact resistance between the carbon nanotubes and induce a metal bond with the copper foil layer (substrate), thereby reducing the contact resistance of the substrate. In addition, the melting action of the low melting point metal particles also serves to reduce the specific resistance by enabling metal bonding between the metal components.

In one embodiment of the present invention, the low melting metal alloy comprises at least two selected from the group consisting of tin (Sn), bismuth (Bi), indium (In), silver (Ag) and cadmium (Cd). It may be an alloy, but is not necessarily limited thereto.

Specifically, the low melting point metal alloy according to the present invention is preferably any one selected from an alloy consisting of tin / bismuth, bismuth / tin / cadmium, indium / tin and indium / tin / bismuth, but is not necessarily limited thereto. .

Specifically, the tin / bismuth alloy may be an alloy composed of 40 to 45 wt% tin and 60 to 55 wt% bismuth; The bismuth / tin / cadmium alloy may be an alloy composed of bismuth 45-50 wt%, tin 15-40 wt% and cadmium 15-40 wt%; The indium / tin alloy may be an alloy composed of 50 to 70% by weight of indium and 50 to 30% by weight of tin; And the indium / tin / bismuth alloy may be an alloy consisting of indium 5-30% by weight, tin 30-60% by weight and bismuth 25-45% by weight.

More specifically, examples of the low melting metal alloys preferred for use in the present invention include 42Sn / 58Bi (number means wt%, melting point (MP) = 141 ° C.), 53Bi / 26Sn / 21Cd (MP = 103 (DegreeC), 70 In / 30Sn (MP = 126 degreeC), 50 In / 50Sn (MP = 117 degreeC), 10 In / 53Sn / 37Bi (MP = 100-123 degreeC) is mentioned.

The low melting point metal alloy may be used by purchasing a commercially available one. Specific products include low-melting metal products sold by MCP Group, Lowden Metals Ltd., RotoMetals Inc., Mitsui Metal Mining Co., Senju Metal Industry Co., Ltd., and Deoksan Hi-Metal Co., Ltd. There is.

In one embodiment of the present invention, the binder may be selected from the group consisting of thermosetting resins, thermoplastic resins, UV curable resins and radical curable resins, and mixtures thereof, but is not necessarily limited thereto.

The thermosetting resin may be selected from the group consisting of epoxy resins, cyanate ester resins, bismaleimide resins, polyimide resins, benzocyclobutene resins, phenol resins, and mixtures thereof, but is not limited thereto. In this invention, an epoxy resin is the most preferable.

The thermoplastic resin may be selected from the group consisting of liquid crystal polyester resins, polyurethane resins, polyamideimide resins, and mixtures thereof, but is not necessarily limited thereto.

The conductive paste according to the present invention is selected from the group consisting of dyes, pigments, thickeners, lubricants, antifoams, dispersants, leveling agents, brighteners, thixotropic agents, flame retardants, oxide removers, organic fillers, inorganic fillers and mixtures thereof. It may further include an additive. The additive may be added in an appropriate amount depending on the purpose and use. In the present invention, it is preferable to add 1 to 7% by weight, but is not necessarily limited thereto.

The oxide remover may remove oxides on the surface of the low melting metal alloy when tin or the like is oxidized. Examples of the oxide remover include materials such as rosin flux, organic flux, and surface treatment agent. The oxide remover is generally commercialized. Moreover, carboxylic acids, such as adipic acid and stearic acid, vinyl ether, etc. can also be used as an oxide remover.

When the said inorganic filler is added, the thermal expansion rate of the electrically conductive paste which concerns on this invention can be reduced. Examples of the inorganic filler include silica, alumina, talc, diatomaceous earth, nanofiller, etc., such as flat plate and amorphous form.

1 to 3 show the operating principle of the conductive paste according to the present invention. 1 shows a conductive paste according to the present invention filled between copper foil layers. The process including the temperature range corresponding to the melting point of the low melting point metal alloy, for example, proceeds the printing process and the sequential curing process of the temporary drying / main drying at 150 ~ 250 ℃.

1 illustrates a temporary drying process. Cross-linking of the binder 14 is started under the temporary drying (80 to 100 ° C.) conditions, whereby the low melting metal alloy particles 13 are formed of the copper foil layer 11 and the carbon nanotubes 12. Contact with each other. Then, as shown in Figure 2, in the main drying (100 ~ 168 ℃) conditions including the melting point temperature of the low melting point metal alloy particles 13, the metal with the carbon nanotube and copper foil layer while melting the low melting point metal particles Metallic bonding is formed. In FIG. 2 the binder is in a semi-cured state (B-stage). 3, the binder is completely cured through a lamination cycle (C-stage).

In particular, in the case of using the alloy particles mainly composed of tin of the low melting point metal alloy of the present invention, it is possible to solve a poor insulation distance (wavy) when stacking the conductive paste due to eutectic properties. In addition, due to the eutectic properties of the tin has the advantage that the interlayer matching of the upper and lower copper foil layer is well made.

As shown in Figures 1 to 3, the conductive paste of the present invention is capable of metal bonding between the metal components due to the melting action of the low melting point metal alloy particles, metal bonding between the copper foil layer and the metal particles. Able to know. This metal bond reduces specific resistance and contact resistance. Therefore, the electrically conductive paste of this invention is a paste which can solve the problem which the conventional electrically conductive paste has-the specific resistance increases because of the binder component.

In addition, the conductive paste of the present invention, since the surface of the carbon nanotubes in contact with the carbon nanotubes can be a metal reaction, there is an advantage that can be implemented simultaneously X-Y interconnection and Z-interconnection through the printing process.

In addition, since the conductive paste of the present invention uses carbon nanotubes at a temperature of 150 to 200 ° C., various problems that occur when growing carbon nanotubes by a method such as CVD at high temperature can be solved.

According to another aspect of the present invention, the present invention provides a printed circuit board using the above-mentioned conductive paste. Specifically, a method of manufacturing a printed circuit board according to an embodiment of the present invention is illustrated in FIGS. 4 to 12. The manufacturing method shown in the drawings is exemplary, and the conductive paste according to the present invention may be used for various printed circuit boards other than those shown in the drawing.

As shown in FIG. 5, the etching resist 22 is laminated | stacked on the copper foil laminated board 21 (S10 of FIG. 4). Then, exposure and development are performed (S20 in FIGS. 6 and 4), a circuit pattern is formed (S3O in FIGS. 7 and 4), and the insulating layer 23 is laminated (S40 in FIGS. 8 and 4). Next, via holes 25 are formed by using a laser, and a plating layer 24 using electroless plating is formed (S50 of FIGS. 9 and 4). Then, the etching resist 26 is stacked thereon (S60 in FIGS. 10 and 4), and the etching resist is removed after the etching resist is removed to correspond to the circuit pattern (S70 in FIGS. 11 and 4). Then, the vias 28 are filled with a paste 27 including carbon nanotubes according to the present invention through a printing process to form vias 28 (S80 of FIGS. 12 and 4).

The electrically conductive paste of this invention is applicable also to a multilayer printed circuit board. In addition, the conductive paste of the present invention can be applied to various substrates such as pad integrated printed circuit boards or landless printed circuit boards.

The invention can be better understood through the following examples, which are intended for purposes of illustration of the invention and are not intended to limit the scope of protection defined by the appended claims.

Example

Examples 1-7 and Comparative Example 1

Multi-walled carbon nanotubes (manufactured by ILJIN) were placed in a solution containing 1: 3 of nitric acid and sulfuric acid at 120 ° C. for 10 hours. Then, the carbon nanotubes were washed with distilled water, a low melting point metal alloy (LMPA) was prepared as shown in Table 1 below, a curing agent was mixed in a conductive paste having a composition as shown in Table 2 below, and a three roll mill (3 Roll). Mill).

Then, the pastes of Examples 1 to 7 and Comparative Example 1 were applied and dried five times by screen printing on the mat surface of the electrolytic copper foil having a thickness of 18 μm, and conical bumps having a bottom diameter of 150 μm and a height of 187 μm were removed. Formed. After prepreg B was placed on this sheet and the prepreg was penetrated, the mat surface of the electrolytic copper foil having a thickness of 18 μm was placed downward, and a stainless plate having a thickness of 2 mm was placed on both sides thereof, and 180 A double-sided copper plate was laminated for 90 minutes under vacuum at 20 ° C., 20 kgf / cm ² , and 2 mmHg. Circuits were formed on this surface to form a daisy chain. Next, the resistance of both ends of the daisy chain was measured by a 4 point probe method, and the minimum initial resistance value of one bump was measured by dividing by the number of bumps 24 in the chain (contact resistance is ignored at this time). . The results are shown in Table 3 below.

Example LMPA Type One 42Sn / 58bi 2 42Sn / 58bi 3 42Sn / 58bi 4 26Sn / 53Bi / 21Cd 5 70In / 30Sn 6 50Sn / 50Sn 7 10In / 53Sn / 37Bi

Example Comparative example One 2 3 4 5 6 7 One CNT (% by weight) 85 85 80 85 85 85 85 90 LMPA (% by weight) 5 10 10 5 5 5 5 - Binder ( epon -862 ) 5 5 5 5 5 5 5 10 Oxide Remover ( RF800NS ) 5 - 5 5 5 5 5 - Initial resistance value (mΩ) 2 5 7 7 7 5 10 20

* epon -862 (Shell Chemical Co., Ltd., Shell Chemical Company )

* RF800NS (Alpha Metals Co., Ltd.)

Reliability test

The conductive paste of Example 1 was tested for reliability of TC (Thermal Cycle), HAST (High Accelerated Temperature / Humidity Test), LLTS, and solder pot, and the results are shown in FIGS. 13 to 16. Indicated. As shown in Figures 13 to 16, it can be seen that the rate of change of resistance vs. initial resistance <± 10%, which is a reliability test criterion, is satisfied.

The reliability verification was generally performed with equipment that is subjected to reliability checks.

As can be seen from the above examples and comparative examples, it can be seen that the conductive paste according to the present invention has excellent electrical conductivity due to low resistance value.

Simple modifications and variations of the present invention can be readily made by those skilled in the art, and all such modifications and variations are intended to be included within the scope of this invention.

1 to 3 are drawings showing the operating principle of the conductive paste according to the present invention.

4 is a flowchart illustrating a method of manufacturing a printed circuit board according to an embodiment of the present invention.

5 to 12 are flowcharts illustrating a method of manufacturing a printed circuit board according to an exemplary embodiment of the present invention.

13 to 16 are graphs showing reliability verification results for a thermal cycle (TC), a high accelerated temperature / humidity test (HAST), an LLTS, and a solder pot for Example 1, respectively.

17 illustrates a typical X-Y interconnection and Z-interconnection.

<Description of the symbols for the main parts of the drawings>

11: copper foil layer 12: carbon nanotube

13: low melting point metal alloy 14: binder

21: copper foil laminated plate 22, 26: etching resist

23: insulating layer 24: plating layer

25: Via Hole

27: paste containing carbon nanotubes according to the present invention

28: Via containing carbon nanotube paste according to the present invention

Claims (14)

As a conductive paste containing carbon nanotubes, Carbon nanotubes; A low melting point metal alloy having any one selected from the group consisting of tin / bismuth, bismuth / tin / cadmium, indium / tin and indium / tin / bismuth and having a melting point of 200 ° C. or less; And a binder, Conductive paste meltable at 150-200 ° C. The method of claim 1, A conductive paste comprising 70 to 90 wt% of the carbon nanotubes, 1 to 25 wt% of the low melting point metal alloy, and 1 to 15 wt% of the binder. The method of claim 1, The conductive paste further comprises a metal particle. The method of claim 3, The metal particles are 1 to 10% by weight conductive paste is included. The method of claim 3, And the metal particles are selected from the group consisting of silver, copper, tin, indium, nickel and mixtures thereof. The method of claim 1, The carbon nanotubes are selected from the group consisting of single wall, multi-wall and mixtures thereof. delete delete The method of claim 1, The tin / bismuth alloy is an alloy composed of 40-45 wt% tin and 60-55 wt% bismuth; The bismuth / tin / cadmium alloy is an alloy consisting of 45-50 wt% bismuth, 15-40 wt% tin and 15-40 wt% cadmium; The indium / tin alloy is an alloy composed of 50 to 70% by weight of indium and 50 to 30% by weight of tin; And the indium / tin / bismuth alloy is an alloy consisting of indium 5-30 wt%, tin 30-60 wt% and bismuth 25-45 wt%. The method of claim 1, The binder is a conductive paste selected from the group consisting of thermosetting resins, thermoplastic resins, UV curable resins and radical curable resins, and mixtures thereof. The method of claim 10, The thermosetting resin is an electrically conductive paste selected from the group consisting of epoxy resins, cyanate ester resins, bismaleimide resins, polyimide resins, benzocyclobutene resins, phenol resins, and mixtures thereof. The method of claim 10, And the thermoplastic resin is selected from the group consisting of liquid crystal polyester resins, polyurethane resins, polyamideimide resins, and mixtures thereof. The method of claim 1, The conductive paste further comprises an additive selected from the group consisting of dyes, pigments, thickeners, lubricants, antifoams, dispersants, leveling agents, brighteners, thixotropic agents, flame retardants, oxide removers, organic fillers, inorganic fillers and mixtures thereof. Conductive paste to be. A printed circuit board comprising the conductive paste according to any one of claims 1 to 6 and 9 to 13.

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